1. Technical Field
The present invention relates to a semiconductor memory, and more particularly, to a memory module and method of mounting a memory device on a printed circuit board (PCB) to form the memory module, which is capable of substantially reducing unnecessary routing space.
2. Description of the Background
Modern computer systems require rapid operating speed and high frequency operation. Computer systems commonly employ memory devices such as DRAMs (Dynamic Random Access Memory devices) as a main system memory. Such DRAM devices have developed into synchronous DRAM (SRAM) devices, double data rate SDRAM devices, and Rambus DRAM (hereinafter, referred to as ‘RDD’) devices, to obtain high performance operation that is required for a computer system.
In an RDD, a plurality of RDDs are arranged in a series array on a bus line of a memory system such as a Rambus system. Operation of respective RDDs is controlled by a packet signal of which signals are sequentially received during a predefined signal section. The respective RDDs input and output data respectively and independently. Currently a RiMM (Rambus inline memory module) that is used as a module of computer system is constructed of RDDs. In the RDDs, consecutive data is provided sequentially from a single data pin, and transmission rate, or bandwidth, is determined by the speed of the consecutively provided data and by the number of data pins.
FIG. 1 illustrates the configuration of a general Rambus system. Referring to FIG. 1, a RiMM applied to a Rambus system is formed by disposing several. RDDs on a common PCB at predefined intervals and by sequentially connecting the RDDs using various packaging technologies that include, for example, interconnects in the form of pins or balls. The RDD is thus obtained and operates under the control of command signals that are synchronized to clock signals and that are transferred through a transmission line that is connected to a controller.
FIG. 2 illustrates a RiMM constructed of existing memory. As shown in FIG. 2, a plurality of RDDs are arrayed on bus lines BUS1, BUS2 and BUS3 of a memory system. To connect a first RDD and a connector tab 21 of the PCB for a memory device formed according to existing packaging technology, a bus line BUS3 is directed straight in an upward direction from the tab 21 and then is bent by 90°, and routed to the first RDD; thus requiring a large amount of routing space in an unpopulated portion 20 of the PCB. Similarly, to connect the last RDD to a connector tab of the PCB, routing space is likewise consumed in a distal, unpopulated portion of the PCB. In other words, modules require routing space in unpopulated portions of both ends of the PCB.
FIG. 3 is a photograph of a RiMM device that includes memory devices that are fabricated according to conventional techniques. With reference to FIG. 3, a portion of bus lines 30 is not connected to the RDD due to a lack of space. As described above, even if a smallest size rule is applied to a limited PCB size, it is difficult to design a RiMM product owing to the difficulty in ensuring routing space on both ends of the PCB. Thus, the product device density is lowered. Any required increase in RiMM size negatively impacts the fabrication cost of a computer system.
In a system environment having many mounted RDDs, a transmission line to form a bus line for connecting between an RDD and a tab on both ends of PCB is necessarily wider than that of a transmission line to form a bus line for connecting between mutual RDDs. A wider bus line is required between the devices and tabs for impedance-matching reasons. When a length of the transmission line forming a thick bus line increases, attenuation of a data signal greatly increases.